1,721,225 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Measurement of Single W Boson Production in ep Scattering
Full text linkA key process in understanding the dynamics of the electroweak interactions in the Standard Model (SM) is single W boson production. One of the most striking signatures of this process at HERA is the observation of events with isolated leptons (electrons or muons) and missing transverse momentum, or ‘ℓ + / PT ’ events. In a data sample collected with the H1 detector corresponding to an integrated luminosity of 481 pb−1, 58 such events are observed for a SM prediction of 57.4 ± 7.3. The purity of the H1 analysis in the signal, dominated within the SM by the W boson production, is at the 75% level. This allowed for the determination of the model-independend production cross section for ℓ+/ PT events σℓ+/ PT = 0.24 ± 0.05 (stat) ± 0.04 (sys) pb, (1.1) which is in agreement with the SM expectation of 0.26 ± 0.04 pb. The measurement of ℓ + / PT events is also used to determine the cross section for single W boson production at HERA σW = 1.23 ± 0.25 (stat) + 0.13 (sys) pb, (1.2) which is in good agreement with the SM expectation of 1.31 ± 0.20 pb. This is the most precise measurement of the single W boson production cross section to date in ep scattering. The single W boson production cross section is sensitive to anomalous values of the coupling parameters dκ and λ that govern the WWγ coupling. The number of observed ℓ + / PT events are used to extract limits on the possible anomalous values of dκ and λ, which have SM expectation values dκ = λ = 0. The following 95% CL single parameter limits are obtained −4.9 < dκ < −2.7 and − 0.8 < dκ < 1.5, (1.3) and −2.9 < λ < 2.9. (1.4) No deviations from the SM are observed. Due to the limited statistics, these limits are not competitive with the corresponding results obtained at LEP and the Tevatron. The W boson is further studied using the charged lepton decay angle in the W boson rest frame. The W boson polarisation fractions F− and F0, for left handed and longitudinally polarised W bosons, respectively, were measured for the first time at HERA. The two-dimensional 68% and 95% CL regions were extracted. In addition, F− and F0 were measured in single parameter fits F− = 0.56 ± 0.16 (stat) + 0.02 − 0.02 (sys), (1.5) F0 = 0.14 ± 0.23 (stat) + 0.01 − 0.01 (sys), (1.6) which is consistent with the SM predictions F−= 0.61 ± 0.01 and F0= 0.17 ± 0.01. These measurements provide a unique test of the SM. The main uncertainty is due to statistics and can be further improved in a future H1/ZEUS combined analysis
The ATLAS inner tracker and the detection of light super-symmetric Higgs bosons
Full text linkWithin the ATLAS-SCT collaboration silicon microstrip detectors with binary readout have been developed for the intermediate layers of the ATLAS tracking and vertexing detectors. Extensive tests of prototype modules in particle beams show that the design meets the stringent requirements. Tests on modules that were previously exposed to a large dose of ionising and non-ionising radiation show that the prototypes maintain an adequate performance after the dose expected during 10 years of LHC operation. The precise reconstruction of particle trajectories and vertices allows to take advantage of the long lifetime of B hadrons to identify jets originating from bottom quarks (b-tagging). This technique can lead to a substantial reduction of the background for many signals. The expected ATLAS b-tagging performance is studied using simulated WH events. In the Minimal Super-Symmetric extension of the Standard Model the Higgs sector consists of five Higgs bosons. The coupling of the neutral Higgs bosons to bottom quarks is strongly enhanced for large values of tan beta. The high rate of h/A/H production in association with bottom quarks opens up decay channels that are not easily detectable in the Standard Model. Here, the decay of h and A bosons into muon pairs is considered. The uncertainties in the rate are discussed, comparing the so-called Matrix Element and shower approaches. While tagging of (one of) the associated b-jets allows a drastic reducion of the dominant Drell-Yan background, the irreducible Zbb background is still considerable. Nevertheless, with a large integrated luminosity (300 fb-1) the h/A -> mumu channel will yield a 5 sigma discovery over an important part of parameter space: tan beta > 14, for 105 < mA < 125
Data Read-out and Bc Production in ATLAS
Full text linkIn this thesis, the design and implementation of the CRUSH is discussed. The maximum input rate as a function of various parameters has been measured. The results have been fitted to yield simple parametrised equations which can be used for modelling purposes. The CRUSH shows good performance, both in a stand-alone test and in a ROB complex setup, and is able to store event fragments at the maximum LVL1 accept rate of ~ 100 kHz
The ATLAS muon spectrometer: commissioning and tracking
Full text linkThe Standard Model is a well established theory for elementary particle physics that describes all known elementary particles and their interactions. Except for gravity all known forces are included: the electromagnetic, weak and strong nuclear force. ATLAS is one of the two general-purpose experiments at the LHC accelerator at CERN, which is a proton-proton collider with an unprecedented nominal center-of-mass energy of 14 TeV. One of its main goals is to study the Standard Model and look for possible new physics beyond this model. Especially searched for, will be the Higgs particle, the last not-measured particle predicted by the Standard Model. Extensions to the Standard Model will be tested, e.g. supersymmetry and theories with extra dimensions. In many of the searches muons with a high transverse momentum will be crucial due to their clean signature in the detector. In this thesis the performance of the muon spectrometer of ATLAS has been studied. Four detector technologies are deployed; the Resistive Plate Chambers (RPC) and the Thin Gap Chambers (TGC) provide the trigger in respectively the barrel and the endcap regions; the precision measurements to measure the momentum are performed by three layers of the Monitored Drift Tube (MDT) chambers and for the inner forward regions by the Cathode Strip Chambers (CSC). An eight-fold toroidal superconducting magnet system provides a magnetic field of typically 0.5 T. With these detectors the muon spectrometer will provide a momentum dependent muon trigger and measure the muon momenta with a resolution between 4% for 10 GeV < pT < 500 GeV and better than 10% for transverse momenta up to 1 TeV. For each muon traversing the muon spectrometer these detectors will produce a number of position measurements. From this set of measurements, the trajectory can be reconstructed. The reconstruction is performed in several steps, first an initial pattern recognition is performed, after which the measurements in the individual chambers are locally fitted into so-called segments. From these segments track candidates are built, which are then fitted. For the initial pattern recognition, an algorithm consisting of a family of global pattern searches based on the Hough transform has been developed. All detector technologies provide a precise measurement for two dimensions (xy or Rz), while the position in the other dimension is less precise. Therefore, the algorithm performs a search in each of the two precision planes, xy and Rz. The resulting two-dimensional patterns are then combined into a three-dimensional pattern. For the Rz-hits a transform is used that accounts for the curvature of the tracks. The algorithm applies several techniques to distinguish patterns in the high background environment of ATLAS. The algorithm assigns a weight to each measurement, depending on the likelihood of it being a noise hit. Depending on the occupancy, special weighting is applied to reduce the cpu usage. It is shown that the algorithm has an excellent efficiency over a wide range of momenta and a low cpu usage in high background. The pattern recognition algorithm is part of the highly modular and recently revised MOORE reconstruction program, which is, besides Muonboy, one of the two muon standalone reconstruction programs in ATLAS. The whole chain of MOORE modules, including the segment reconstruction, segment combining and tracking has been described in detail. Its performance is demonstrated on simulated dimuon decays of Z0-bosons and J/ψ mesons. The performance metrics include efficiency, fake rates and momentum resolution. The total track efficiency and momentum resolution are well understood and competitive to the Muonboy programme. Misidentified track rates have been discussed and are shown to be under control. For the commissioning of the ATLAS detectors, cosmic muons are deployed. To utilise the possibilities of these muons completely, the tracking needs to be changed and optimised. In particular the initial pattern recognition needs to be altered to account for non-pointing tracks. For this, dedicated Hough transforms have been developed. Furthermore, several adaptations have been made to the MOORE reconstruction programme to achieve a similar efficiency as the collision muons. On simulated cosmic muon samples it has been shown that the reconstruction is well understood for different categories of events. For each of these categories, it has been shown that MOORE has a better performance than Muonboy, especially for muons with large impact parameters with respect to the interaction point. Cosmic muons have been recorded in the cavern since 2005 and the setup has been gradually extended. In 2008 all ATLAS detectors were present in the readout. For the muon spectrometer, differences between simulated and real cosmic ray muon data have been explained, with a focus on the reconstruction strategy. It has been shown that the MDT detector performance and MOORE segment and tracking reconstruction are robust and efficient for real cosmic muon data. Furthermore, it is shown that MOORE is currently the best reconstruction programme for cosmic muon data
- …
